The Amateur Amateur: Pouncing on Digital Modes
By Gary Hoffman, KB0H
I was ready to
transmit on PSK31 but didn't want anyone to hear me if I messed up.
July 17, 2005
, I recounted how I started investigating digital
modes, got an interface to connect my computer with my transceiver
and obtained free software to make it all work. Now let me tell you
what I saw and heard.
There are a
number of digital mode freeware and shareware programs available. I
just because I thought it looked pretty (DigiPan
is another popular--and free--PSK31 software package). I've found
more options than I'll ever
need, but when I'm bored I try some of them just to see what happens.
So far I haven't damaged anything.
The HamScope software "waterfall" display, showing
multiple conversations (the vertical bars) on one radio frequency.
Anyway, I spent a
lot of time just fiddling around and gazing at the waterfall--the
visual display of what I heard on the speaker. One nice thing about
typical digital mode software is being able to hear and "see"
the signal at the same time.
what that electric line noise looks like!" I'd say
I'd never been
adept enough to work the ancient oscilloscope that someone had given
to me, so this sort of thing was all new territory.
Eventually I got
around to looking for actual digital-mode signals. I was most
interested in picking up PSK31
transmissions. FYI: PSK stands for P
which is the modulation method used to generate the signal. The 31 is
the bit rate, which, not to be too fussy, is actually 31.25 Hz. PSK31
signals are not hard to find. Just as with voice modes, if the bands
are open, someone will be transmitting a digital signal.
For those who've
never had the experience, let me take a moment to describe operating
in PSK31 mode. PSK31 is a keyboard-to-keyboard mode. In really simple
terms, you type a message, and it appears on the receiving station's
computer screen. When the other op responds, his or her message
appears on your computer screen. From a completely non-technical
standpoint it's a little like being in an Internet chat room.
hear on your transceiver is a sort of chirpy-warbly sound. Its pitch
depends on what part of the audio spectrum the sender uses. Since a
PSK31 signal occupies very little bandwidth you can pack a lot
of signals onto one radio frequency. On a good day you can, in fact,
tune to the favorite PSK31 hangout on 20 meters, 14.070 MHz (±2
kHz), and "see" several conversations going on at the same
time. Regrettably you can't monitor them all at once, although
and some other popular software packages will let you
copy two messages at the same time.
Oops! The extra cable does do something after all.
The day finally
came when I felt confident enough to try sending my own message.
Rather than trying to jump into an existing conversation I started
transmitting on an unused part of the audio spectrum. For that
matter, it was an unused part of the radio
there were no
conversations taking place. In fact, the whole
band was dead. I was ready to transmit, all right, but I didn't want
anyone to hear me if I messed up.
Well, it was kind
of cool. The waterfall display changed dramatically, showing only my
transmission. And I quickly figured out that I had to stop
or my rig would keep on pumping out my
lack of keystrokes--an idling signal. Within a few minutes, however,
I found the proper way to end my transmissions automatically.
One thing puzzled
me, though. Although the waterfall display showed my transmissions
blasting away into the ether, I didn't notice any change in what I
was hearing from my transceiver's speaker. Okay, you've figured it
out already, but I've given you all the clues. At the time I was
focused on what I was seeing
rather than what I was hearing
While I hate to admit it, it took me a few minutes to figure out that
I wasn't actually transmitting anything. The computer said I was, but
the transceiver sat there placidly, not sending a thing. And again,
this is embarrassing, but remember that extra plug
mentioned in Part One of this story? It suddenly became clear what it
was supposed to do.
A card from Argentina confirming my first DX on PSK31.
Okay, let me
back up for a just a second. On my left side is the computer. On my
right side is the transceiver. The transceiver has one cable plugged
into its DATA port. This connects to a conversion box that splits
into three other wires that connect to the PC. One cable goes into
the speaker port and another to the microphone port on my sound card.
And that's where my brain stopped working:
Hey, I had
wires to receive data and to send data, what more did I need? Oh,
yeah. What about
that third cable? Well, as it turns out, that
one lets the PC tell the transceiver when to transmit and when to
receive. In other words, it acts like the push-to-talk button.
Even though no
one saw me, my face was still red as I plugged that "extra"
cable, which connects to the PC's serial (COM) port.
I soon got over
my little faux pas
and started transmitting for real. And
quickly enough I was joining in conversations. My first PSK31 contact
was with Wen Johnson, K7RME, in Tucson, Arizona. A week later I
failed in my attempt to check in to a multistate earthquake drill,
but I did succeed in making contact with the group running the drill
via PSK31. And the week after that
I made my first DX
PSK31 contact with Juan Bilbao, LU5DIT, in Argentina.
Oh yeah! I can
tell that digital modes are going to be a lot
Editor's note: ARRL member Gary Hoffman, KB0H, lives in Florissant,
Missouri. He's been a ham since 1995. Hoffman says his column's name
-- "The Amateur Amateur" -- suggests the explorations of a
rank amateur, not those of an experienced or knowledgeable ham. His
wife, Nancy, is N0NJ. Hoffman has a ham-related
Readers are invited to contact the author via e-mail,
© 2005 American Radio Relay League